* If searchers list is empty, adds the searcher; otherwise, replaces the first searcher.
     *
     * @param searcher the RankFusionSearcher to set as the main searcher
     */
    public void setSearcher(final RankFusionSearcher searcher) {
        if (searchers.isEmpty()) {
            searchers.add(searcher);
        } else {
            searchers.set(0, searcher);
        }
    }

    /**